Vibrating structures, including electric machines such as motors and generators, are widely employed in industrial and commercial facilities. These machines are relied upon to operate with minimal attention and provide for long, reliable operation. Many facilities operate several hundreds or even thousands of such machines concurrently, many of which are integrated into a large interdependent process or system. Like most machinery, at least a small percentage of such are prone to failure. The majority of such failures can be attributed to either mechanical failures and/or thermal failures of the machine insulation.
Other than normal aging, failures are typically due to: poor or no maintenance; improper application (e.g., wrong enclosure, excessive loading, etc.); and improper installation (e.g., misalignment, bad power, inverter mismatch, etc.). Even with normal aging failures, it is desirable to provide low cost failure prediction information for such machines.
Depending on the application, the failure of a machine in service can possibly lead to system or process down time, inconvenience, and possibly even a hazardous situation. Thus, it is desirable to diagnose the machinery for possible failure or faults early in order to avoid such problems.
Vibration analysis is an established technique for determining the health of mechanical components in rotating machinery such as motors. To obtain vibration data from machinery and other structures, accelerometers as well as associated sampling and filtering techniques are often employed. Larger machines and/or systems may also employ proximity detectors in addition to or instead of accelerometers to determine vibration.
In structures such as electric machines, multiple axis detection and multiple location sensing typically are necessary to properly diagnose vibration in the machine. Thus, in many cases, multiple sensors and detectors are required to be located on the machine. As more and more sensing elements are added to the machine, cost associated therewith increases. Also, for critical machines, additional failure detection mechanisms may be needed because the sensing elements themselves can fail.
The accelerometers typically employed utilize a moving mass which is coupled with other mechanical and electrical components to generate an electrical signal (e.g., magnetically or capacitively coupled). The resulting electrical signal must then be transmitted via electrical wires where it may be filtered, digitized, analyzed (e.g., FFT analysis) and appropriate control and data recording performed. Due to the low signal levels and the amount of data to be transferred, the length of the signal wires are generally limited and the wire lengths are minimized where possible. In an electrically noisy environment, such as an electric motor, more costly shielded cables are used and there will be further processing performed very near the sensor or integral with the sensor.
Typical accelerometers will therefore employ signal wires which contain a varying voltage or current which indicate the vibration experienced at the sensor. In addition, several more wires must also be routed to the sensor to provide power to the accelerometer. The additional wires must be routed through and attached to the structure and represent a possible location for shorting or sparking or for picking up electrical noise which may influence the sensor readings.
Consequently, there is a strong need in the art for a system and/or method for detecting vibrations in structures that requires minimal components, requires less wiring, provides for high noise immunity, provides for lower maintenance, and provides for lower costs.